Experimental and theoretical study of PEG/natural clay-based hybrids properties: Role of molecular weight

Abstract

The present study in this article is designed firstly for a physicochemical and mineralogical characterization of a clay mineral from the Meknes region. The natural clay was first crushed (agate mortar), sieved (63μm) and purified, then characterized to determine the different physicochemical parameters as well as the minerals it contains. Secondly, hybrids based on this natural clay and the polymer (Polyethylene glycol: PEG) were produced using the direct intercalation process. In our study, we were interested in elucidating the role of the PEG molecular weight variation on the final product. These composites were observed using different techniques at different scales for a multi-scale characterization of their microstructure. The obtained results indicate a homogeneous mineralogical composition characterized by the predominance of clay minerals (smectite, kaolinite, and illite) associated with other minerals such as quartz and calcite. Moreover, the measurements of the physico-chemical parameters show an average cation exchange capacity (29mequi/100g) and a specific surface of about 204m2/g. The transmission electron microscopy confirms the formation of the intercalated structures by insertion of PEG chains in good conformity with the X-ray diffraction (XRD) findings. Fourier transform infrared (FTIR) analysis reports the presence of new PEG-related vibrational bands in the hybrids, this confirms the adsorption of PEG chains. We find that there is a consensus that HPEG8000 hybrids are more suitable and stable and that 8000g/mol is the optimal molecular weight. Finally, the XRD results were used to follow the inter-layer distance of the phases versus the molecular weight of PEG. These results show a very good agreement with the theory developed by using the De Gennes scaling laws.